DTC P0301 - GTR
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Bentley Continental GT; AMG GT
On misfires, most EMSs build in both a counter and a clock. To set a CEL there would need to be a number of misfires within a defined period of time. If the time is exceeded, then the ECU erases those counts and starts counting over. This is done to eliminate false counts, which can happen on misfires. I'll bet none of the 301s listed above are actual misfires.
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2017 GCV, 2019 JEEP TH-E
On misfires, most EMSs build in both a counter and a clock. To set a CEL there would need to be a number of misfires within a defined period of time. If the time is exceeded, then the ECU erases those counts and starts counting over. This is done to eliminate false counts, which can happen on misfires. I'll bet none of the 301s listed above are actual misfires.
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Misfires are interesting and why any EMS design uses counter/timers.
How does the ECU know there was a misfire?
It can verify there is a good electrical circuit going to the coil, and it can verify it sent a signal voltage at the correct time. It can also verify the coil worked correctly, electrically. But how does it know the spark plug fired? There is no sensor sitting inside the cylinder. The next sensor inline that gives any feedback to the combustion event is the O2 sensor. The ECU knows where it is via the crank position sensor and cam position sensors (if equipped), then it can register anomalies in the exhaust pulses and correlate that to one of the previous combustion events. So, if there is an unusual drop (as in raw or unburned fuel) in the amount of oxygen coming from a voltage spike delivered by the O2 sensor, the ECU concludes a misfire has occurred and registers ONE occurrence. If, when that same time comes around again and there is no adverse pulse, then the ECU is beginning to forget (forgive) that single event as an outlier.
Something about O2 sensors, this is the crudest sensor in the car. I use widebands when I tune. The difference between a wideband measuring oxygen levels in the exhaust and an O2 sensor doing it is like the difference between a scalpel and a battle axe. That is the reason the EMS doesn't take the first or even few misfire counts seriously.
There could be all kinds of reasons for the occasional "stray" misfire:
These could be happening on startup and since this is the #1 cylinder, it could be that cold exhaust pulse just hits the O2 sensor right at warmup, but too cold to register a clean exhaust.
An O2 sensor that is becoming "flakey" or "lazy" in its operating range (but works fine in operating temps)
The opposite and an O2 sensor that begins to operate flakey at the high temp extreme.
A slightly dirty or sticking fuel injector on the #1 cylinder (more common than realized).
A spark plug that performs (for a moment) poorly in its heat range (more likely on the cold side as the engine is warming up).
And a bunch of others that start to get really rare.
It is almost never the obvious as in bad spark plug or bad coil.
Bottom line is - chasing a single misfire that doesn't set a CEL (falls short of the ems designed count/time) is pretty much a waste of time.
Another way of thinking about it - if your engine is running at 2000 RPM the ECU sees and validates the #1 cylinder has fired correctly 1000 times every minute. To have a single event cross a threshold and then 999 other good ones and beyond...hardly a concern to the EMS, but it dutifully counts the mishap.
Sorry for the long draw.
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reignz (03-01-2021)
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realien (03-01-2021)
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Took it to the dealer as it popped a CEL, apparently this is a known issue on the GT, P030185, P030022. PER TIP DOC# GI54.21-P-061775, Software update and scn coding on engine module, power traiasn moudule and trany module due to software issue.
They said to monitor it now if it comes back they will change all spark plugs out of warranty under some Critical failure procedure?
They said to monitor it now if it comes back they will change all spark plugs out of warranty under some Critical failure procedure?